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2010 Annual Science Report

Arizona State University Reporting  |  SEP 2009 – AUG 2010

Astrophysical Controls on the Elements of Life, Task 1: High-Precision Isotopic Studies of Meteorites

Project Summary

The evolution of habitable planets may be affected by the injection of short-lived radionuclides, produced by supernova explosions, early in solar system history. In this task we are finding evidence of such injection in some of the earliest Solar System materials (calcium-aluminum-rich inclusions) and constraining the timing of early Solar System events.

4 Institutions
3 Teams
4 Publications
0 Field Sites
Field Sites

Project Progress

A major research project under Task 1 is the identification and Pb-Pb dating of calcium-aluminum-rich inclusions (CAIs) containing fractionated unknown nuclear (FUN) effects. We have obtained a suite of documented and well-characterized CAIs from the Allende and Vigarano carbonaceous chondrites (provided to us by Dr. Glenn MacPherson), and are initiating isotopic investigations of these samples with the goal of identifying possible candidates of FUN CAIs. Specifically, we successfully developed the analytical protocols for high-precision measurements of Ti isotopes by laser ablation and solution analyses in the Isotope Cosmochemistry and Geochronology Laboratory at ASU, and have initiated Ti isotopic analyses on the suite of documented Allende CAIs. The purpose of this project is to utilize Ti isotope compositions of CAIs as an indicator for the identification of FUN CAIs. Additionally, we obtained preliminary Pb-Pb ages for two of the Vigarano CAIs.

A second project, which has important implications for the Pb-Pb dating of FUN CAIs, relates to the investigation of uranium isotope variations in CAIs. High-precision Pb-Pb dating has relied on the assumption of an invariant 238U/235U ratio, and the goal of this investigation was to verify this assumption for meteoritic materials. Graduate Student Greg Brennecka, working with Meenakshi Wadhwa and Ariel Anbar, therefore analyzed thirteen different CAIs from the Allende carbonaceous chondrite and found variations of up to ~3.5 per mil in the 238U/235U ratio (relative to the terrestrial standard). These variations in the 238U/235U ratio correlate with Th/U and Nd/U ratios in these CAIs, suggesting that they are the result of decay of 247Cm in the early Solar System. This work was published in Science in January 2010; as a follow-up, we began high precision U isotopic analyses of a suite of carefully selected meteoritic samples to better constrain other possible mechanisms that could result in U isotopic variations in meteoritic materials.

Finally, a third project on the Fe-Ni systematics in achondritic meteorites was initiated; this has implications for the initial abundance of 60Fe in the early Solar System.

Publications

  • Brennecka, G. A., Weyer, S., Wadhwa, M., Janney, P. E., Zipfel, J., & Anbar, A. D. (2009). 238U/235U Variations in Meteorites: Extant 247Cm and Implications for Pb-Pb Dating. Science, 327(5964), 449–451. doi:10.1126/science.1180871

  • Bouvier, A., Wadhwa, M., Bullock, E. & MacPherson, G.  (2010).  Pb-Pb dating of a CAI from the reduced CV3 chondrite Vigarano.  Meteoritics and Planetary Science, 45: Abstract.
  • Brennecka, G.A., Wadhwa, M., Janney, P.E. & Anbar, A.D.  (2010).  Towards reconciling early Solar System chronometers: The 2388U/235U ratios of shondrites and D’Orbigny pyroxenes.  Lunar and Planetary Science Conference.  The Woodlands, TX.
  • Spivak-Birndorf, L., Wadhwa, M. & Janney, P.E.  (2010).  60Fe-60Ni isotope systematics of buld ureilites.  Meteoritics and Planetary Science, 45: Abstract.